doc: Fork me image should be full url

Author: isaacs

doc/index.html

@@ -32,7 +32,7 @@
         ><a href="api/" class="button" id="docsbutton">API Docs</a>
         </div>
 
-        <a href="http://github.com/joyent/node"><img class="forkme" src="images/forkme.png" alt="Fork me on GitHub"></a>
+        <a href="http://github.com/joyent/node"><img class="forkme" src="http://nodejs.org/images/forkme.png" alt="Fork me on GitHub"></a>
     </div>
 
     <div id="quotes" class="clearfix">